Wave division multiplexer arrangement for small cell networks

ABSTRACT

A passive optical network includes a central office providing subscriber signals; a fiber distribution hub including an optical power splitter and a termination field; and a drop terminal. Distribution fibers have first ends coupled to output ports of a drop terminal and second ends coupled to the termination field. A remote unit of a DAS is retrofitted to the network by routing a second feeder cable from a base station to the hub and coupling one the distribution fibers to the second feeder cable. The remote unit is plugged into the corresponding drop terminal port, for example, with a cable arrangement having a sealed wave division multiplexer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 14/468,913,filed Aug. 26, 2014, which issued as U.S. Pat. No. 9,438,513, whichapplication claims the benefit of provisional application Ser. No.61/869,984, filed Aug. 26, 2013, and titled “Wave Division MultiplexerArrangement for Small Cell Networks,” which applications areincorporated herein by reference in their entirety.

BACKGROUND

Fiber optic telecommunications technology is becoming more prevalent asservice providers strive to deliver higher bandwidth communicationcapabilities to customers/subscribers. The phrase “fiber to the x”(FTTX) generically refers to any network architecture that uses opticalfiber in place of copper within a local distribution area. Example FTTXnetworks include fiber-to-the-node (FTTN) networks, fiber-to-the-curb(FTTC) networks, and fiber-to-the-premises (FTTP) networks.

FTTN and FTTC networks use fiber optic cables that are run from aservice provider's central office to a cabinet serving a neighborhood.Subscribers connect to the cabinet using traditional copper cabletechnology, such as coaxial cable or twisted pair wiring. The differencebetween an FTTN network and an FTTC network relates to the area servedby the cabinet. Typically, FTTC networks have cabinets closer to thesubscribers that serve a smaller subscriber area than the cabinets ofFTTN networks.

In an FTTP network, fiber optic cables are run from a service provider'scentral office all the way to the subscribers' premises. Example FTTPnetworks include fiber-to-the-home (FTTH) networks andfiber-to-the-building (FTTB) networks. In an FTTB network, optical fiberis routed from the central office over an optical distribution networkto an optical network terminal (ONT) located in or on a building. TheONT typically includes active components that convert the opticalsignals into electrical signals. The electrical signals are typicallyrouted from the ONT to the subscriber's residence or office space usingtraditional copper cable technology. In an FTTH network, fiber opticcable is run from the service provider's central office to an ONTlocated at the subscriber's residence or office space. Once again, atthe ONT, optical signals are typically converted into an electricalsignal for use with each subscriber's devices. Of course, to the extentthat subscribers have devices that are compatible with optical signals,conversion of the optical signal to an electrical signal may not benecessary.

FTTP networks include active optical networks and passive opticalnetworks. Active optical networks use electrically powered equipment(e.g., a switch, a router, a multiplexer, or other equipment) todistribute signals and to provide signal buffering. Passive opticalnetworks use passive beam splitters instead of electrically poweredequipment to split optical signals. In a passive optical network, ONT'sare typically equipped with equipment (e.g., wave-division multiplexingand time-division multiplexing equipment) that prevents incoming andoutgoing signals from colliding and that filters out signals intendedfor other subscribers.

FIG. 1 illustrates a FTTP network 100 deploying passive fiber opticlines. As shown, the network 100 can include a central office 101 thatconnects a number of end subscribers 105 in a network. The centraloffice 101 can additionally connect to a larger network, such as theInternet (not shown) and a public switched telephone network (PSTN). Thevarious lines of the network 100 can be aerial or housed withinunderground conduits.

The network 100 also can include fiber distribution hubs (FDHs) 103having one or more optical splitters (e.g., 1-to-8 splitters, 1-to-16splitters, or 1-to-32 splitters) that generate a number of distributionfibers that may lead to the premises of an end user 105. In typicalapplications, an optical splitter is provided prepackaged in an opticalsplitter module housing and provided with a splitter output in pigtailsthat extend from the module. The splitter output pigtails are typicallyconnectorized with, for example, SC, LC, or LX.5 connectors. The opticalsplitter module provides protective packaging for the optical splittercomponents in the housing and thus provides for easy handling forotherwise fragile splitter components. This modular approach allowsoptical splitter modules to be added incrementally to FDHs 103 asrequired.

The portion of the network 100 that is closest to central office 101 isgenerally referred to as the F1 region, where F1 is the “feeder fiber”from the central office 101. The portion of the network 100 closest tothe end users 105 can be referred to as an F2 portion of network 100.The F2 portion of the network 100 includes distribution cables routedfrom the FDH 103 to subscriber locations 105. For example, thedistribution cables can include break-out locations 102 at which branchcables are separated out from the main distribution lines. Branch cablesare often connected to drop terminals 104 that include connectorinterfaces for facilitating coupling of the fibers of the branch cablesto a plurality of different subscriber locations 105 (e.g., homes,businesses, or buildings). For example, fiber optic drop cables can berouted directly from a breakout location 102 on the distribution cableto an ONT at a subscriber location 105. Alternatively, a stub cable canbe routed from a breakout location of the distribution cable to a dropterminal 104. Drop cables can be run from the drop terminal 104 to ONT'slocated at premises 105 located near the drop terminal 104.

Distributed Antenna Systems (DAS) also are becoming more prevalent. DASare used to provide wireless service (e.g., cell phone, WIFI, etc.)within a given geographic area. DAS include a network of spaced-apartantenna nodes optically or electrically connected to a common controllocation (e.g., a base station). Each antenna node typically includes anantenna and a remote unit (i.e., a radio head, a remote transceiver,etc.).

DAS enable a wireless cellular service provider to improve the coverageprovided by a given base station or group of base stations. In DAS,radio frequency (RF) signals are communicated between a host unit andone or more remote units. The host unit can be communicatively coupledto one or more base stations directly by connecting the host unit to thebase station using, for example, electrical or fiber telecommunicationscabling. The host unit can also be communicatively coupled to one ormore base stations wirelessly, for example, using a donor antenna and abi-directional amplifier (BDA). One or more intermediate devices (alsoreferred to here as “expansion hubs” or “expansion units”) can be placedbetween the host unit and the remote units in order to increase thenumber of remote units that a single host unit can feed and/or toincrease the hub-unit-to-remote-unit distance.

RF signals transmitted from the base station (also referred to here as“downlink RF signals”) are received at the host unit. The host unit usesthe downlink RF signals to generate a downlink transport signal that isdistributed to one or more of the remote units. Each such remote unitreceives the downlink transport signal and reconstructs the downlink RFsignals based on the downlink transport signal and causes thereconstructed downlink RF signals to be radiated from at least oneantenna coupled to or included in that remote unit.

A similar process is performed in the uplink direction. RF signalstransmitted from mobile units (also referred to here as “uplink RFsignals”) are received at each remote unit. Each remote unit uses theuplink RF signals to generate an uplink transport signal that istransmitted from the remote unit to the host unit. The host unitreceives and combines the uplink transport signals transmitted from theremote units. The host unit reconstructs the uplink RF signals receivedat the remote units and communicates the reconstructed uplink RF signalsto the base station. In this way, the coverage of the base station canbe expanded using the DAS.

One general type of DAS is configured to use optical fibers tocommunicatively couple the host unit to the remote units and/orexpansions hubs. However, such a fiber-optic DAS typically makes use ofdedicated optical fibers that are deployed specifically to support thatDAS.

SUMMARY

Features of the present disclosure relate to methods and systems forefficiently and cost effectively distributing fiber optic communicationsservices to a local area while concurrently supporting a DistributedAntenna System.

Aspects of the disclosure are related to a passive optical networkincluding first and second signal sources, a fiber distribution hubreceiving signals from both sources, and a drop terminal receiving bothsignals from the fiber distribution hub. The drop terminal outputs thefirst signals at one or more ports and outputs the second signals at oneor more other ports.

Other aspects of the disclosure are related to a cable arrangement thatfacilitates feeding a small cell covering multiple bands and/or multipleproviders with a single dark fiber in a passive optical network. In someimplementations, the cable arrangement includes a sealed wave divisionmultiplexer having a connectorized input fiber and multipleconnectorized output fibers. Each output fiber carries one or more ofthe optical signals carried over the input fiber, each optical signalhaving its own wavelength.

The connectorized end of the input fiber of the cable arrangement can beplugged into an output port of a drop terminal (e.g., a multi-serviceterminal) of a passive optical network. For example, the input fiber canbe plugged into an empty port of a drop terminal that otherwise serviceshomes, businesses, or other buildings of end subscribers.

The output fibers of the cable arrangement can be plugged into inputports (Rx) and output ports (Tx) of a DAS remote access unit (e.g.,remote radio head). Each pair of ports (Rx, Tx) corresponds with adifferent provider (e.g., a mobile phone service provider) and/ordifferent telecommunications standard (e.g., LTE, 4G, and 3G, such asGSM, CDMA, EDGE, UMTS, DECT, WiMAX). For example, a first pair of fiberscan bi-directionally carry a signal corresponding to a first band for afirst provider; a second pair of fibers can bi-directionally carry asignal corresponding to a second band for the first provider; and athird pair of fibers can bi-directionally carry a signal correspondingto a first band for a second provider.

In certain implementations, one or more of the optical connectors of thecable arrangement can be hardened connectors. For example, the inputfiber can be terminated by a hardened (i.e., environmentally sealed)connector and plugged into an output port of a drop terminal mounted toa power line pole, light pole, or other such outdoor structure. Theoutput fibers can be terminated by hardened connectors and plugged intoports of an outdoor remote unit for a DAS. In other implementations, theinput and/or output connectors of the cable arrangement can benon-hardened (i.e., not environmentally-sealed). For example, suchoutput connectors can be plugged into an indoor remote access unit.

A variety of additional inventive aspects will be set forth in thedescription that follows. The inventive aspects can relate to individualfeatures and to combinations of features. It is to be understood thatboth the forgoing general description and the following detaileddescription are exemplary and explanatory only and are not restrictiveof the broad inventive concepts upon which the embodiments disclosedherein are based.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the description, illustrate several aspects of the presentdisclosure. A brief description of the drawings is as follows:

FIG. 1 is a schematic diagram of an FTTP network deploying passive fiberoptic lines;

FIG. 2 is a schematic diagram of an FTTP network including a dropterminal and FDH;

FIG. 3 is a schematic diagram of the FTTP network of FIG. 2 with a basestation and remote unit retrofitted to the network;

FIG. 4 illustrates the drop terminal and remote unit of FIG. 3 mountedto a pole in the field; and

FIG. 5 is a schematic diagram of a cable arrangement suitable forconnecting the drop terminal and the remote unit of FIGS. 3 and 4.

DETAILED DESCRIPTION

Reference will now be made in detail to the exemplary aspects of thepresent disclosure that are illustrated in the accompanying drawings.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like structure.

An aspect of the present disclosure relates to a fiber optic networkincluding at least one fiber distribution hub (FDH) and a plurality ofdrop terminals (i.e., multi-service terminals) that are opticallyconnected to the FDH by optical distribution cables. The fiber opticnetwork can be used to connect end subscribers (e.g., subscribers 105 ofFIG. 1) to a central office (e.g., central office 101 of FIG. 1). Remoteradio heads of a Distributed Antenna System (DAS) also can be connectedto the fiber optic network.

For example, a first feeder cable can be used to connect a first signalsource (e.g., at a central office) to an FDH; drop cables can be used toconnect the subscriber locations to the drop terminals; and distributioncables can be used to connect the drop terminals to the FDH to provide afirst type of service. A second feeder cable can be used to connect asecond signal source (e.g., at a base station) to the FDH; drop cablescan be used to connect the antenna nodes to the drop terminals; and thedistribution cables connect the drop terminals to the FDH to provide asecond type of service. In certain implementations, the antenna nodesand the second source can be retrofitted to an existing optical network.In some such implementations, one or more of the same components (e.g.,FDH, distribution cables, drop terminals) can be used for both types ofservices.

FIG. 2 is a schematic diagram of an example optical network 200 thatconnects a first signal source (e.g., a central office) 210 to endsubscribers 250. A first feeder cable 212 connects the first signalsource 210 to an FDH 220. One or more fibers (e.g., single-mode fibers)of the first feeder cable 212 are routed to a passive optical splitter222, which splits signals carried over the feeder cable 212 ontosplitter pigtails 225. The splitter pigtails 225 are optically coupledto fibers 235 of a distribution cable 230, which are routed out of theFDH 220. For example, within the FDH 220, connectorized ends 226 of thesplitter pigtails 225 can be routed to a termination field 228 at whichthey are optically coupled to connectorized ends 232 of the distributionfibers 235.

The splitter 222 includes at least one passive optical power splitter.Passive optical power splitters (e.g., 1 to 8 splitters, 1 to 16splitters, 1 to 32 splitters, 1 to 64 splitters, etc.) split signalsfrom one to many and combine signals from many to one without providingany wavelength filtration. In the case of a 1 to 8 splitter, each of thesplit signals has ⅛^(th) the power of the input signal.

The distribution cable 230 is routed from the FDH 220 to at least onedrop terminal 240. The fibers 235 of the distribution cable 230 areoptically coupled to output ports 245 of the drop terminal 240. Dropcables 255 extend between the output ports 245 of the drop terminal 240and the end subscribers 250. For example, each drop cable 255 canconnect one of the end subscribers (e.g., a house, a business, abuilding, etc.) to one of the drop terminal ports 245. In someimplementations, the drop terminal 240 has between two and sixteen ports245. In certain implementations, the drop terminal 240 has between fourand twelve ports 245. In an example, the drop terminal has six ports245. In an example, the drop terminal has eight ports 245.

In some implementations, a drop terminal 240 may have one or more emptyports 245′ that are not connected to subscribers 250. If a newsubscriber joins the network (i.e., requests the first type of service),then a drop cable 255 can be plugged into one of the empty ports 245′ toextend service to the subscriber 250. Of course, a drop terminal port245 may become empty be disconnecting or adjusting the connection of anexisting subscriber 250.

According to some aspects of the disclosure, one or more remote units ofa DAS can be coupled to the optical network 200. For example, as shownin FIG. 3, one or more of the remote units (e.g., remote radio heads)260 can be connected to one of the empty drop terminal ports 245′. Theempty port 245′ can be connected to a second signal source 215 via asecond feeder cable 216 at the FDH 220. The second signal source 215includes one or more lasers capable of transmitting beams of light overnarrow bands with narrow gaps between the bands. Each remote unit 260includes an antenna 265 for wirelessly broadcasting the optical signalscarried over the second feeder cable 216.

In some implementations, the base station 215 is located within thecentral office 210 (e.g., see FIG. 3). In other implementations, thebase station 215 can be located remote from the central office 210. Thebase station 215 includes active electrical components for managing thevarious signals fed back and forth between the antenna nodes 265 and thebase station 260. For example, the base station 215 can include aplurality of transceivers for receiving and transmitting signals and apower amplifier for amplifying the signals. The base station 215 can beconfigured for any one or more telecommunications standards including 3G(e.g., GSM, EDGE, UMTS, CDMA, DECT, WiMAX, etc.), LTE, and 4G. In oneembodiment, the base station 215 includes optical multiplexers (e.g.,wavelength division multiplexers) to join signal into a multiplexedsignal transmitted through the second feeder cable 216 to the FDH 220and to separate the multiplexed signal received from the FDH 220 intoseparate signals to be carried back over the second feeder cable 216.

At the FDH 220, one or more connectorized ends 218 of the second feedercable 216 can be plugged into the termination field 228. In certainimplementations, the second feeder cable 216 is not split before beingplugged into the termination field 228 (i.e., the optical signalscarried by the second feeder are not passed through an optical powersplitter). The connectorized end of a distribution fiber 235 routed toan empty drop terminal port 245′ can be optically coupled to the secondfeeder connectorized end 218 at the termination field 228 (see FIG. 3).Accordingly, the empty port 245′ receives the optical signals (e.g., themultiplexed optical signal) carried over the second feeder 216 from thebase station 215.

At the drop terminal 240, a drop cable 255 can be plugged into an emptyport 245′. When plugged in, the drop cable 255 receives the multiplexedsignal carried over the distribution fiber 235 coupled to the secondfeeder cable 216. An opposite end of the drop cable 255 is coupled tothe remote unit 260. In certain implementations, the drop cable 255 isruggedized (e.g., enclosed and/or sealed against environmentalcontamination). In certain implementations, multiple remote units 260can connect to one drop terminal 240 with respective drop cables 255(e.g., see the top drop terminal 240 shown in FIG. 3). In certainimplementations, signals from the second feeder 216 are provided tomultiple drop terminals 240 (e.g., see FIG. 3). For example, certaintypes of second feeders 216 can include multiple feeder fibers.

FIG. 4 shows one example drop terminal 240 deployed in the field. In theexample shown, the drop terminal 240 is mounted to one of a plurality ofpoles 280 (e.g., telephone pole, light pole, etc.). Various cables 285(e.g., power cables, other optical cables, etc.) are routed between thepoles 280. The routed cables 285 include the distribution cable 230. Insome implementations, a connectorized end of a distribution cable 230 isplugged into an input port of the drop terminal 240. In otherimplementations, the distribution cable 235 includes a connectorizedinput stub of the drop terminal 240 routed along the poles 280 (and/orthrough underground conduits) to the FDH 220. In some implementations,one or more drop cables 255 can be routed from the drop terminal 240 toend subscribers 250.

In the example shown, an outdoor remote unit 260 also is mounted to thepole 280. In other implementations, however, the remote unit 260 can bemounted to a different pole 280 or at a different location adjacent thepole 280. In still other implementations, the remote unit 260 can bemounted to the pole 280 and the drop terminal 240 can be mounted to anadjacent location. In some implementations, a drop cable 255 can berouted between the empty port 245 and the remote unit 260. In otherimplementations, the remote unit 260 can be connected to the empty port245′ using a cable arrangement 300 (FIG. 4) that multiplexes anddemultiplexes the optical signals passed between the port 245 and theremote unit 260.

FIG. 5 illustrates one example cable arrangement 300 suitable for use inconnecting a remote unit 260 to a drop terminal 240. The cablearrangement 300 includes a wave division multiplexer (WDM) 320 disposedbetween a single optical fiber 310 and multiple optical fibers 330. Insome implementations, between two and sixty-four fibers 330 extend fromthe WDM 320. In certain implementations, between four and thirty-twofibers 330 extend from the WDM 320. In certain implementations, betweeneight and twenty-four fibers 330 extend from the WDM 320. In an example,about sixteen fibers 330 extend from the WDM 320. In otherimplementations, any desired number of fibers 330 can extend from theWDM 320.

The WDM 320 demultiplexes optical signals carried by the single opticalfiber 310 from the drop terminal 240 and routes the demultiplexedsignals to the multiple optical fibers 330. Each optical fiber 330carries an optical signal having a different wavelength (or wavelengthband) from the optical signals carried on the other fibers 330. The WDM320 also multiplexes optical signals carried by the multiple opticalfibers 330 from the remote unit 260 and routes the multiplexed signal tothe single optical fiber 310. In certain implementations, the WDM 320includes a passive WDM. In an example, the WDM 320 is a standard WDM. Inanother example, the WDM 320 is a coarse wave divisional multiplexer(CWDM). In another implementation, the WDM 320 is a dense wavedivisional multiplexer (DWDM), which can separate out more signals thana CWDM.

Certain example standard WDMs provide up to eight channels in the thirdtransmission window (1530 to 1565 nm). Certain example DWDM use the sametransmission window, but with denser channel spacing. For example,certain DWDMs can use forty channels at 100 GHz spacing or eightychannels with 50 GHz spacing. A CWDM uses increased channel spacing.Accordingly, eight channels on an example single fiber CWDM can use theentire frequency band between second and third transmission window (1260to 1360 nm and 1530 to 1565 nm).

In some implementations, the wave division multiplexer 320 of the cablearrangement 300 is sealed from the outside environment. For example, thewave division multiplexer 320 can be overmolded or otherwise enclosed ina protective closure or seal 340. In certain implementations, portionsof the single optical fiber 310 and multiple optical fibers 330 also areincluded within the sealed enclosure 340. In certain implementations,the single fiber 310 and multiple fibers 330 are separately ruggedized(e.g., have hardened outer jackets, etc.).

A distal end of the single optical fiber 310 is terminated by an opticalconnector 315 to enable the distal end to be plugged into the empty port245′ at the drop terminal 240. Distal ends of the multiple opticalfibers 330 also are terminated by optical connectors 335 to enable thedistal ends to be plugged into ports at the remote unit 260.Non-limiting examples of optical connectors 315, 335 suitable forterminating the optical fibers 310, 330 include SC-connectors,LC-connectors, LX.5-connectors, ST-connectors, and FC-connectors. Incertain implementations, the optical connectors 315, 335 terminating theoptical fibers 310, 330 are hardened optical connectors. Non-limitingexamples of hardened optical connectors are disclosed in U.S. Pat. Nos.7,744,288 and 7,113,679, the disclosures of which are herebyincorporated herein by reference.

In some implementations, the multiple optical fibers 330 of the cablearrangement 300 can be plugged into ports (e.g., receive ports (Rx) andtransmit ports (Tx)) of a DAS remote access unit 260. In certainimplementations, the optical signals passing through each port have adifferent wavelength or wavelength band than the optical signals passingthrough the other ports. In certain implementations, pairs of opticalfibers 330 can be terminated at duplex optical connectors and pluggedinto corresponding receive and transmit ports. Each pair of ports (Rx,Tx) corresponds with a different provider (e.g., a mobile phone serviceprovider) and/or different telecommunications standard (e.g., LTE, 4G,and 3G, such as GSM, CDMA, EDGE, UMTS, DECT, WiMAX).

For example, a first pair of fibers 330 can bi-directionally carry asignal corresponding to a first band for a first provider; a second pairof fibers 330 can bi-directionally carry a signal corresponding to asecond band for the first provider; and a third pair of fibers 330 canbi-directionally carry a signal corresponding to a first band for asecond provider. In other implementations, each individual fiber can beassociated with a separate band and/or provider.

The above specification, examples and data provide a completedescription of the manufacture and use of the composition of theinvention. Since many embodiments of the invention can be made withoutdeparting from the spirit and scope of the invention, the inventionresides in the claims hereinafter appended.

What is claimed is:
 1. A wave division multiplexing cable arrangement comprising: a sealed enclosure defining an interior; a wave division multiplexer disposed within the sealed enclosure, the wave division multiplexer being configured to multiplex optical signals received at an input line onto a plurality of ruggedized output cables having distal ends accessible from an exterior of the sealed enclosure, the wave division multiplexing arrangement forming part of a cable having a first end at a ruggedized optical connector terminating a distal end of the input line and an opposite second end at ruggedized optical connectors terminating the distal ends of the output cables; and a drop terminal having an input and a plurality of outputs; wherein the ruggedized optical connector terminating the distal end of the input line of the wave division multiplexer is plugged into one of the outputs of the drop terminal.
 2. The wave division multiplexing arrangement of claim 1, wherein the wave division multiplexer is a coarse wave division multiplexer.
 3. The wave division multiplexing arrangement of claim 1, wherein the input line extends through the sealed enclosure to provide the optical signals to the wave division multiplexer.
 4. The wave division multiplexing arrangement of claim 3, wherein the input line is ruggedized.
 5. The wave division multiplexing arrangement of claim 3, wherein the input line is connectorized.
 6. The wave division multiplexing arrangement of claim 1, wherein the output cables include ruggedized cables extending outwardly through the sealed enclosure.
 7. The wave division multiplexing arrangement of claim 6, wherein distal ends of the output cables are terminated by ruggedized optical connectors.
 8. The wave division multiplexing arrangement of claim 1, wherein the wave division multiplexer is overmolded to form the sealed enclosure.
 9. The wave division multiplexing arrangement of claim 1, wherein the ruggedized output cables are plugged into ports of a separate housing.
 10. The wave division multiplexing arrangement of claim 9, wherein the housing is a remote unit.
 11. The wave division multiplexing arrangement of claim 9, wherein the ports include a transmit port and a receive port.
 12. The wave division multiplexing arrangement of claim 1, wherein the wave division multiplexer has eight output cables.
 13. The wave division multiplexing arrangement of claim 1, wherein the wave division multiplexer has between two and sixty-four outputs.
 14. The wave division multiplexing arrangement of claim 13, wherein the wave division multiplexer has between four and thirty-two outputs.
 15. The wave division multiplexing arrangement of claim 13, wherein the wave division multiplexer has between eight and twenty-four outputs.
 16. The wave division multiplexing arrangement of claim 1, wherein the wave division multiplexer is a dense wave division multiplexer.
 17. The wave division multiplexing arrangement of claim 1, wherein pairs of the output cables are terminated at duplex optical connectors. 